From owner-freebsd-amd64@FreeBSD.ORG Wed Feb 27 21:51:17 2008 Return-Path: Delivered-To: freebsd-amd64@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 9AE3C1065676 for ; Wed, 27 Feb 2008 21:51:17 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from speedfactory.net (mail.speedfactory.net [66.23.216.219]) by mx1.freebsd.org (Postfix) with ESMTP id 0E8748FC1A for ; Wed, 27 Feb 2008 21:51:16 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from server.baldwin.cx (unverified [66.23.211.162]) by speedfactory.net (SurgeMail 3.8s) with ESMTP id 233622210-1834499 for multiple; Wed, 27 Feb 2008 16:49:12 -0500 Received: from localhost.corp.yahoo.com (john@localhost [127.0.0.1]) (authenticated bits=0) by server.baldwin.cx (8.14.2/8.14.2) with ESMTP id m1RLp8xV036786; Wed, 27 Feb 2008 16:51:09 -0500 (EST) (envelope-from jhb@freebsd.org) From: John Baldwin To: freebsd-amd64@freebsd.org Date: Wed, 27 Feb 2008 15:28:12 -0500 User-Agent: KMail/1.9.7 References: <443D814E-04F3-411C-9DF9-E799A39FAEB3@gmail.com> <20080227184522.GE83599@server.vk2pj.dyndns.org> In-Reply-To: <20080227184522.GE83599@server.vk2pj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200802271528.12444.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-2.0.2 (server.baldwin.cx [127.0.0.1]); Wed, 27 Feb 2008 16:51:09 -0500 (EST) X-Virus-Scanned: ClamAV 0.91.2/6014/Wed Feb 27 15:42:51 2008 on server.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-4.4 required=4.2 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.1.3 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on server.baldwin.cx Cc: Subject: Re: "freebsd-amd64" X-BeenThere: freebsd-amd64@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Porting FreeBSD to the AMD64 platform List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Feb 2008 21:51:17 -0000 On Wednesday 27 February 2008 01:45:23 pm Peter Jeremy wrote: > On Wed, Feb 27, 2008 at 07:34:48AM -0600, Jeff Isaac wrote: > >doodle with, not BIOS), BUT, from a general knowledge perspective, what > >advantages does virtual 86 mode have over real mode? Essentially, why did > >the FreeBSD project choose the virtual implementation? More portable? > >Easier to write? None of the above? Thanks! :) > > The kernel run in 32-bit protected mode. Switching between protected > mode and real mode requires a reasonable degree of voodoo which does > not currently exist in the kernel (the loader handles the initial real > to protected transition and the kernel then never leaves protected mode). > Plus you need to either ensure that exceptions/interrupts won't occur > or handle them in real mode. OTOH, virtual86 mode is part of the > hardware - you create a task descriptor and set the VM86 bit. Any > exceptions etc are delivered to the kernel. And VM86 mode was designed for running real mode code from protected mode safely. The problem is that since a certain OS from the pacific northwest just invokes the BIOS from real mode BIOS vendors have become lazy since their QA usually consists of WHQL or something similar. -- John Baldwin